Existing cellular network systems have enjoyed great popularity in recent years. At various times, the channels that carry the voice communications of the cellular system may be idle (i.e. no signal transmission over the channel at a particular time). These unused or idle voice channels may be utilized for other communication such as data communication. In particular, an overlay system network utilizing unused or idle voice channels for digital data communication is desirable. Cellular Digital Packet Data (CDPD) is an overlay system which provides mobile datagram service utilizing existing cellular telephone networks. The CDPD system allows digital data transmission over idle channels of an already existing cellular system. A consortium of cellular communication carriers prepared and released in 1993 a specification entitled "Cellular Digital Packet Data System Specification." The specification suggests that monitoring devices known as "sniffers" can be used to determine the current usage of allocated non-CDPD channels.
It is thus desirable to provide a detection system for use with an overlay system which detects channel occupancy in a cellular system so that the transmission of digital data over the overlay system does not interfere with the voice communications or any system diagnostics occurring in the underlying cellular network system.